The present invention generally relates to high intensity discharge (xe2x80x9cHIDxe2x80x9d) lamps, arc tubes, and methods of manufacture.
HID lamps such as metal halide and mercury lamps have found widespread use in lighting large outdoor and indoor areas such as athletic stadiums, gymnasiums, warehouses, parking facilities, and the like, because of the relatively high efficiency, compact size, and low maintenance of HID lamps when compared to other lamp types. Metal halide lamps are often preferred because of the efficiency of such lamps in producing white light.
HID lamps include an arc tube supported within an outer lamp envelope. The arc tube comprises a generally tubular body of light transmissive material such as quartz or ceramic material which forms a hermetically sealed light emitting chamber containing the lamp fill material and an inert fill gas. Generally, there are several types of arc tube bodies for HID lamps. One type of arc tube body is a xe2x80x9ccylindricalxe2x80x9d body formed from quartz tubing having the diameter of the generally cylindrical arc tube chamber in which the chamber is formed by pinch-sealing the end portions of the tubing. Another type of arc tube body is a xe2x80x9cformedxe2x80x9d body which is formed from quartz tubing of a much smaller diameter in which a bulbous light emitting chamber is formed by expansion under internal pressure between two end portions having the much smaller diameter of the tubing. The aforementioned types of arc tube bodies are used in forming xe2x80x9cdouble-endedxe2x80x9d arc tubes, i.e. arc tubes having spaced apart electrodes with one sealed at each end. The arc tubes for HID lamps may also be xe2x80x9csingle-endedxe2x80x9d arc tubes having a bulbous chamber sealed at its only end.
An arc tube includes a pair of spaced apart electrodes between which the arc is established during operation of the lamp. In a double-ended arc tube, an electrode lead assembly is sealed in each end portion of the arc tube. The electrode lead assembly typically comprises a tungsten electrode, a molybdenum foil, and an outer molybdenum lead.
In the manufacture of double-ended arc tubes for HID lamps, either cylindrical body or formed body arc tubes, the light emitting chamber is sealed by positioning the electrode lead assemblies in each end portion of the arc tube body, heating a portion of each end portion, and then shrinking or pinching the heated portion around the electrode lead assembly positioned therein to thereby fix the position of the assembly relative to the arc tube body and to form a hermetic seal. The temperature of the heated portions typically reaches about 2000xc2x0 C. or more. At these high temperatures, the metallic components of the electrode lead assembly positioned within the end portion are highly susceptible to corrosion when exposed to an uncontrolled atmosphere such as the air surrounding a factory production line, and any corrosion may significantly degrade the performance of the lamp and possibly lead to the mechanical failure of the lead assembly. Thus it is important to avoid exposure of the electrode lead assemblies to an uncontrolled atmosphere when the temperature of the assemblies is elevated during the manufacturing process.
In the context of the present invention, an xe2x80x9cuncontrolled atmospherexe2x80x9d is any atmosphere other than one in which the composition of the atmosphere is strictly controlled such as the atmosphere in a glove box. The atmosphere surrounding a factory production line is considered to be an uncontrolled atmosphere even though there may be some control of the temperature, humidity, particulate content etc. of the atmosphere.
In the manufacture of HID lamps, the light emitting chamber of the arc tube body is dosed with solid lamp fill material such as one or more metal halides. This material is susceptible to moisture contamination when exposed to an uncontrolled atmosphere which significantly degrades the performance of the lamp. Thus in the manufacturing process, it is also important to avoid exposure of the solid lamp fill material to contaminating atmospheres.
In a known method of making arc tubes for HID lamps, an arc tube body is formed from vitreous material such as quartz. A fill/exhaust tube is then fused near the longitudinal center of the body where the light emitting chamber will be formed. The exhaust tube provides a means for communication between the interior of the chamber and the exterior of the arc tube body. The electrode lead assemblies are positioned and then pinch-sealed in the end portions of the arc tube body. During the pinch-sealing process, anon-reactive gas is introduced into the chamber through the fill/exhaust tube to prevent the exposure of the metallic components of the electrode lead assemblies to air when the components are heated during the sealing process, to thereby prevent corrosion of the metallic components. In the context of this invention, a xe2x80x9cnon-reactivexe2x80x9d gas is a gas which is non-reactive with respect to the lamp components including, for example, the electrode lead assemblies and lamp fill material.
Once the ends of the arc tube body are sealed, the solid fill material and mercury are introduced into the chamber through the fill/exhaust tube. An inert fill gas is then introduced into the chamber at the desired fill pressure and the fill/exhaust tube is fused closed to thereby hermetically seal the chamber.
This prior art method suffers from several disadvantages including the substantial disadvantage that the chamber wall includes an irregularity at the point where the fill/exhaust tube was attached and then fused closed and tipped off. This irregularity may cause a cold spot on the wall of the chamber where halides will condense during operation of the lamp, and the condensation of halides may have a significant effect on the color uniformity of the light emitted from the lamp. The irregularity in the chamber may also disturb the light emitted from the chamber and the condensed halides may create shadows, making it difficult to control and direct the light. This is especially undesirable in optical systems such as fiber optics, projection display, and automotive headlamps. These disadvantages have a greater detrimental effect on lower wattage lamps which are smaller and where the irregularity includes a greater portion of the chamber wall.
A further disadvantage of the arc tube having a fused closed fill/exhaust tube applies to arc tubes mounted within a protective shroud or within tubular outer envelopes. The portion of the fill/exhaust tube which has been fused closed protrudes radially from the chamber wall of the arc tube. Thus a cylindrical shroud or tubular envelope must be of a larger diameter to envelope an arc tube with a radially protruding tip.
The prior art has developed methods of making xe2x80x9ctip-lessxe2x80x9d arc tubes to obviate the deficiencies of the arc tube having a fused closed fill/exhaust tube. However, the prior art methods of making tipless arc tubes require the use of a controlled environment during at least some of the process steps.
Generally, the known methods of making tipless arc tubes include the steps of providing an arc tube body; positioning and then sealing an electrode lead assembly in one end portion of the arc tube body; introducing the solid lamp fill material and an inert fill gas into the interior of the body through the remaining open end portion of the body; and positioning and then sealing another electrode lead assembly in the remaining open end portion of the body to thereby form a hermetically sealed light emitting chamber.
To prevent oxidation of the metallic components of the first electrode lead assembly during the sealing process of the first end portion, it is known to introduce a non-reactive gas into the interior of the body through the other end portion to thus create a flow of non-reactive gas past the lead assembly during the sealing process. This prevents exposure of the metallic components to a reactive atmosphere such as moisture laden air during the sealing process. The non-reactive gas is commonly introduced into the interior of the body by conventional means such as fitting a hose over the end of the open end portion or inserting a probe into the interior of the body through the open end portion.
The interior of the body is then filled with a non-reactive gas through the open end portion prior to the introduction of the solid lamp fill material. The lamp fill material is typically stored in a dry non-reactive atmosphere and thus may be introduced into the interior of the body without contamination.
To prevent oxidation of the metallic components of the second electrode lead assembly during the sealing process of the second end portion, the prior art teaches that the interior of the arc tube body must be isolated from an uncontrolled atmosphere once the solid fill material and mercury are introduced into the interior of the arc tube body and the second electrode lead assembly is positioned in the remaining open end portion.
The prior art teaches that the interior of the arc tube may be isolated from an uncontrolled atmosphere by either (i) placing the arc tube body in a controlled atmosphere such as a glove box as taught in U.S. Pat. No. 5,108,333 to Heider et al. dated Apr. 28, 1992 or (ii) connecting the open end to a vacuum system which provides the necessary seal as taught in U.S. Pat. No. 5,505,648 to Nagasawa et al. dated Apr. 9, 1996. As illustrated by the prior art, one end portion of the arc tube body must be long enough to enclose the entire electrode lead assembly when the assembly is positioned within the end portion. Once the arc tube is isolated, the arc tube body is filled with the inert fill gas at the desired pressure and then the end portion is fused closed to the outside of the electrode lead assembly to enclose the entire assembly within the body. The arc tube may then be removed from the glove box or vacuum system and the second end portion is sealed by shrinking or pinching, after which the excess portion of the end portion may be removed to expose the outer lead of the electrode lead assembly.
The prior art methods suffer from the significant disadvantage of the requirement for isolating the arc tube body from the uncontrolled atmosphere. This has generally required the use of a glove box or vacuum system. Such methods are complex and difficult to automate.
Accordingly, it is an object of the present invention to obviate many of the deficiencies of the prior art and provide a novel HID lamp, arc tube and method of making arc tubes.
It is another object of the present invention to provide a novel arc tube and method of making arc tubes for HID lamps which obviates the need to perform any process steps within a controlled atmosphere.
It is a further object of the present invention to provide a novel arc tube and method of making tipless arc tubes for HID lamps in which the arc tube remains open to an uncontrolled atmosphere during the step of finally sealing the arc tube.
It is yet another object of the present invention to provide a novel arc tube and method of making tipless arc tubes for HID lamps in which communication of an inert fill gas with an uncontrolled atmosphere such as air is maintained until the arc tube is hermetically sealed.
It is yet a further object of the present invention to provide a novel arc tube and method of making arc tubes for HID lamps which obviates the need to remove a portion of the end portion to expose the outer portion of the electrode lead assembly.
It is still another object of the present invention to provide a novel arc tube and method of making arc tubes for HID lamps in which each end portion of the arc tube body has substantially the same length as the end portions of the finished arc tube.
It is still a further object of the present invention to provide a novel apparatus for extending the tubular opening formed by the end portion of an arc tube body and method of making arc tubes for HID lamps.
It is often desirable to obtain a final fill gas pressure which is significantly below atmospheric pressure at substantially room temperature, i.e., pressures below 500 torr. Final fill gas pressures below about one-half atmosphere are common and may be as low as about 30 torr. A fill pressure of about 100 torr is common in metal halide lamps. In order to obtain such final subatmospheric fill pressures, the prior art uses mechanical means to evacuate the interior of the arc tube to the desired pressure prior to hermetically sealing the interior of the arc tube, i.e., by fusing closed the fill/exhaust tube or shrinking or pinching the remaining open end portion in a tipless arc tube. Such methods require the use of expensive pumps and/or vacuum systems, are complex, and difficult to automate.
The patent to Heider et al. discloses that a xe2x80x9cslightxe2x80x9d under-pressure of the fill gas may be obtained by heating the fill gas and fusing closed the open end portion within a glove box and then removing the arc tube from the glove box to shrink or pinch seal the remaining unpinched end portion. Heider et al. disclose raising the temperature of the fill gas by only 100xc2x0 C. prior to fusing closed the arc tube to obtain a slight under-pressure when the fill gas cools. If the fill gas is heated at atmospheric pressure, a temperature differential of 100xc2x0 C. will provide a final fill gas pressure of greater than 500 torr when the arc tube is sealed and cooled. There is no disclosure in Heider et al. that a significantly subatmospheric fill pressure, i.e., a pressure less than 500 torr, may be obtained by this process, or that the fill gas temperature may be controlled outside of a glove box while open to an uncontrolled atmosphere.
Accordingly, it is yet another object of the present invention to provide a novel arc tube and method of making arc tubes for HID lamps which obviates the need to mechanically evacuate the arc tube to obtain a significantly subatmospheric fill pressure.
It is still another object of the present invention to provide a novel arc tube and method of making arc tubes for HID lamps in which the temperature of the fill gas is controlled prior to sealing the arc tube in an uncontrolled atmosphere.
It is yet another object of the present invention to provide a novel arc tube and method of making arc tubes for HID lamps having significantly subatmospheric fill pressure in which there is no pressure differential at the time of sealing.